Abacus



FIG. 1 is a top plan view of an abacus showing my new design, the bottom view being substantially identical thereto;

FIG. 2 is a side elevational view of the abacus shown in FIG. 1, the opposite side being substantially identical thereto; and

FIG. 3 is an end elevational view of the abacus shown in FIG. 1, the opposite end being substantially identical thereto. 

The ornamental design for an abacus, substantially as shown and described. 